Improvement in the enzymatic hydrolysis of biofuel substrate by a combined thermochemical and fungal pretreatment

Abstract

Pretreatment is a critical step in the enzymatic conversion of lignocellulosic substrate to sugars. A unique pretreatment sequence involving thermochemical treatment (steam explosion) followed by biological treatment (fungal exposure) was evaluated for Pinus radiata as a biofuel substrate. The effect of biological treatment using the white rot Trametes versicolor was investigated on control (sapwood blocks) and steam-exploded wood (SEW) for changes in the profile of fungal enzyme activity and lignocellulose composition. The results indicated that compared to blocks, Trametes versicolor expressed more lignocellulose-degrading enzymes when grown on SEW for 6 and 12 weeks. After fungal exposure, the biomass was mixed with a commercial enzyme cocktail for enzymatic hydrolysis. The maximum conversion of biomass to sugars was obtained for Trametes versicolor-treated SEW, with a yield of 4.80 g of glucose l−1, which is greater compared to that obtained from non-fungal-treated SEW (3.80 g of glucose l−1) and Trametes versicolor-treated sapwood blocks (0.80 g of glucose l−1). Examination by microscopy suggests relative increase in the porosity of SEW after fungal treatment, and compositional analysis indicates reduction in lignin content. Both these factors are likely to contribute to the improved hydrolysis of SEW.